Before the introduction of digital photography to the modern digital world, photographs were made by exposing light sensitive photographic films and applying chemical photographic processes to the films in darkrooms to develop and stabilize images. Such exposure and chemical processing together with the physical structure of the film made the traditional photographs look different than today's digital images. One such difference is elimination of film grain in digital photographs. Film grain is a random optical texture that appears in film during the development process. The grains seen in the traditional photos are actually physical structures of the photosensitive particles in the film which have a direct relationship with the film speed or the sensitivity of camera's sensor to a given amount of light (the “ISO”). Because faster films inherently need larger photo-sensitive crystals, the faster the film speed is, the bigger the grain particles need to be to capture more photons.
Despite the fact that grain is an artifact, it has a very distinctive look and many people lament the loss of this element of the photography experience. Film grain gives an artistic and authentic look to the photograph, in particular to black and white photos. Additionally, if a photo looks blurry, film grain can ameliorate the level of blurriness in the photo. In digital cameras, the closest physical equivalents to film grain are the individual elements of the image sensor (e.g., a charge-coupled device (“CCD”) cell). Unfortunately, pixels from a digital image sensor are organized in straight lines. These straight lines' artifacts may be more irritating to the viewer rather than pleasing as the randomly arranged film grains are. For these reasons, many new image-editing applications have tried to simulate the grain effect of traditional photography in digital photos.
Many of current image-editing applications apply a film grain overlay to the digital image, which essentially adds film noise characteristics to the digital image. However, overlaying film grain often affects dark and bright tonal regions of the digital image. For instance, superimposed graininess often alters the depth of black in the image and is disturbingly visible (appearing artificial) in the brighter tonal region of the image. As a result, the graininess created by simply overlaying film grain on the digital image is often not as visually pleasing as the film grain produced in a natural and traditional process. Additionally, in many of the media-editing applications that are currently available in the market, the grain layer that is generated to be applied to the photo is a static layer (i.e., is not generated dynamically) that has many additional artifacts such as streaks, bars, and other types of noise. These additional and undesired artifacts are mostly generated and appear during the grain layer generation process.